Conventional third generation (3G) and fourth generation (4G) wireless systems use radio access technologies (RATs) that employ orthogonal multiple access (OMA) as multiple access techniques, such as code division multiple access (CDMA) in 3G and orthogonal frequency division multiple access (OFDMA) in 4G. OMA techniques involve transmitting to multiple user equipments (UEs) with full power, but a split bandwidth, for example, via the frequency division of OFDMA, the code division of CDMA, or time division (e.g., in time division multiple access (TDMA)). However, mobile data traffic is expected to increase exponentially over the next decade, outstripping the ability of OMA technologies to meet mobile data traffic demands.
Multiple access refers to how a network device (e.g., an eNB) multiplexes multiple users through limited resources, such as a time resource, frequency resource, spatial resource or other network spectrum resources such as physical resource blocks (PRBs) or the like for wireless or mobile communications. Multiple access is one of the key design aspects of cellular networks, which often significantly affects performance metrics such as throughput, the number of supportable users, latency, etc. The choice of the multiple access scheme is often driven by ease of implementation and main applications like data, voice, small packets, etc. In general, multiple access can be broadly divided classified into orthogonal and non-orthogonal schemes. In OMA, different users are allocated orthogonal or non-conflicting resources in time, frequency or both. In the absence of inter-user interference, low-complexity detection schemes can be employed at the receiver. In fourth generation mobile systems, OFDMA and single carrier frequency division multiple access (SC-FDMA) schemes are used for multiple access, which are examples of orthogonal schemes. Unlike OMA, in non-orthogonal multiple access schemes (NOMA), users share resources and receivers might employ advanced multi-user detection schemes to retrieve data. Examples of NOMA can be CDMA, low Density Spreading (LDS), SCMA, etc. Next generation mobile communication is supposed to support a wide variety of traffic—low latency, delay tolerant, small packets, huge packets, etc.
Next generation mobile communications are predicted to support a wide variety of traffic—low latency, delay-tolerant, small packets, huge packets, etc. Current Long Term Evolution Advanced (LTE-A) is not necessarily designed to support all these applications simultaneously. However, multiple access schemes can be employed with a focus on small packet enhancements, for e.g., machine type communications (MTC), machine-to-machine (M2M), gaming, etc. Signaling overhead, latency and complexity become major design considerations when optimizing uplink transmission of small data packets because of the payload to control overhead ratio. Some multiple access schemes can be engineered to enjoy the benefit of minimal change from existing Long Term Evolution (LTE) systems, while providing benefits in terms of user multiplexing, latency reduction and downlink/uplink control overhead reduction.